1. Field of the Invention
This invention relates generally to the determination of the location of an individual based upon data collected from magnetometers placed in the podiatric region and more particularly to determining the location of a person or robot in a space lacking benchmarks.
2. Background and Prior Art
The determination of a person""s exact location has been a challenge throughout history.
Landmarks in the form of the rivers and mountains sufficed for primitive societies. Highway markers resolved the task for later travelers. Celestial navigation based on the sextant and accurate chronometers made possible marine navigation. All of these methods rely upon fixed points of reference and the person defines his location by reference to the location of the fixed reference point.
A more difficult problem is posed when the only fixed reference point is the point of departure. The problem is raised when a person or a robot must enter a closed location without interior reference points or when the person or robot cannot communicate the relationship to reference points to persons outside the location.
Examples of this condition are rescue persons entering a burning building or robots entering a damaged nuclear reactor.
Pedometers based upon counting the number of steps taken are well known but cannot define direction and must be calibrated for a person""s stride. Electronic pedometers such as that disclosed in U.S. Pat. No. 5,724,265 to Hutchings use accelerometers and rotational sensors together with a small computer to calculate speed, distance, etc.
Dead-reckoning devices for vehicles using multiple sensors to determine speed and heading are disclosed in U.S. Pat. No. 5,075,693 to McMillan et al. and U.S. Pat. No. 5,764,014 to Jakeway et al. These devices measure distance from wheel rotation, ground track sensors and obtain direction using a magnetometer. Problems with systemic and non-systemic errors in such systems are described in University of Michigan Technical Report UM-MEAM-94-22 by Borenstein and Feng.
A dead-reckoning system for pedestrians is disclosed in U.S. Pat. No. 5,583,776 to Levi et al. and uses an accelerometer to measure footsteps. The device is calibrated for the user and the results routinely corrected using data from a GPS receiver. Indoor use would preclude use of GPS and be subject to the same (or worse) errors as described by Bornstein et al.
Magnetometers are instruments used to measure magnetic fields. Particularly useful for navigation are flux-gate or flux-valve magnetometers which find use in compasses and avionics. Using the magnetic poles of the earth, a three-axis magnetometer can detect direction, pitch and yaw in an aircraft. The development of microelectronic processing elements renders information from magnetometers immediately useful and more accurate.
It is a first object of this invention to provide a means for measuring the movement of a person in a space lacking good reference points. It is a second object of this invention to provide a means for advising a person of his location relative to a starting point. It is a third object of this invention to provide a record of a person""s movement. It is a fourth object of this invention to provide a means for others to monitor the position of a person within an enclosure when visible reference points are limited or non-existent.
These and other objectives are obtained by attaching small magnets to a person""s feet and monitoring the movement of these magnets using 3-dimensional magnetometers in conjunction with a computerized monitoring system. The results may be displayed for the user or communicated to persons at a distance. By use of this invention, firefighters in burning buildings can be located and workers in other maze-like settings may be followed.